Andy Fawkes, headteacher of Linchfield Community Primary School, Deeping St James, revealed that over half of its Year 6 pupils were below the Government’s expected standard for reading, writing and maths based on the results of SATs (Standard Assessmen Tests) taken in May.

In a letter to parents, Mr Fawkes said: “early indications show that 51 per cent of pupils have not met the expected standard.”

Two years ago, the Department for Education announced that it was toughening up primary school SATs which test pupils’ abilities in maths, reading, grammar, punctuation and spelling.

Mr Fawkes said: “I was simply stunned at the results before me as they had plummeted.

“In some areas, we appeared to be above national expectations yet, in many ways, we seemed hugely below our achievements in previous years.

It breaks my heart that I have to tell the majority of children that they did not meet the expected primary school standard and are not ‘secondary ready’

“I was devastated, not for me but for your children as I know that we have hugely dedicated and talented staff.”

The school was rated good in all areas by Ofsted after an inspection last November, although a report said that progress at Key Stage 2 was “not yet outstanding because still not enough pupils make greater than expected progress in reading, writing and mathematics”.

But Mr Fawkes said: “Our results are slightly better than the national results in many areas and, having discussed our results with Lincolnshire (County Council), early indications are that we have outperformed our county results too.

“Yet, it breaks my heart today as their headteacher that I have to tell the majority of your children that they did not meet the expected primary school standard and are not ‘secondary ready’, potentially facing SATs retakes in Year 7 through no fault of their own.”

A Department for Education spokesman said: “SATs are designed as a measure of schools, rather than of individual pupils, and the purpose of SATs is to be a measure of progress.

“As far as individuals are concerned, children do not pass or fail SATs and although there is an expected standard, there is absolutely no implication for children who do not reach it.”

Meanwhile, Education Secretary Nicky Morgan defended the tougher SATs as evidence of having “raised the bar on what counts as a good enough standard for our children by the end of primary school”.

Mrs Morgan said: “Nothing is more important than ensuring that young people master the basics of reading, writing and mathematics early on.

“The simple truth is that if they don’t, they’ll be left playing catch up for the rest of their lives.

“That’s why, as part of this Government’s commitment to delivering real social justice, we have raised the bar on what counts as a good enough standard in the 3Rs for our children by the end of primary school.”